Unilateral pneumonectomy in laboratory animals induces a stimulus to the growth of the remaining lung such that lung volume greatly increases above normal. It is proposed to measure and quantitate the extent of new growth and to determine in what regions of the bronchial tree and parenchyma it has occurred. The main thrust of the research is to ascertain the effects of air pollutant gases on this accelerated lung development and to determine whether growth is impaired on exposure to air pollutants in concentrations found in urban environments. The characterization of this "stimulated" lung growth and development in control animals and in animals exposed to ozone, and other oxidants, will derive from measurements of pulmonary function, from quantitative morphometry and from light and electron microscopy. The experimental design offers the advantage of investigating the effects of environmental stress on a compromised organ that consists of both mature tissue and tissue in a state of sudden and forced development. In this respect, the findings may have particular significance in the areas of neo-natal growth and development and lung function and structure following pneumonectomy in the human.